The track record for Democrats is far longer than for Republicans, with Democrats winning six of the last seven presidential races. Not only does a 17-point victory in the primary boost Mr. Obama's confidence, so does the fact that Illinois is an adjoining state. Still, the state has a fondness for mavericks, which gives Mr. McCain a glimmer of hope.

Almanac of American Politics Profile

Wisconsin has been seriously contested in seven of the last eight presidential elections, and has voted narrowly for the Democratic nominee in six of them. The margins have been exceedingly narrow in the last two: 5,708 votes for Al Gore in 2000, 11,384 for John Kerry in 2004. The state was inundated by ads and lawn signs in both campaigns, and was especially heavily contested in 2004; Kerry stumbled when he came to Green Bay on Sept. 1 and referred to “Lambert Field” (it’s Lambeau Field, as any Cheesehead can tell you). But Kerry perhaps atoned by abjuring the Northeast Dairy Compact and by spending three days later that month doing debate preparation in Spring Green.

In both these races some historic patterns were reversed. Bush carried metro Milwaukee, which casts about one-third of the state’s votes, by narrow margins both times, thanks to big margins in the suburbs; while he ran far behind his father’s 1988 showings in the nation’s biggest metropolitan areas, he ran ahead in metro Milwaukee. But Gore and Kerry carried many historically Republican or marginal counties in western Wisconsin, just as they carried many rural counties across the Mississippi River in eastern Iowa. Indeed, this was the only rural part of the country where Gore and Kerry carried large numbers of counties and ran ahead of Democratic norms. Their biggest percentage margins were in Madison’s Dane County and in Menominee County, which is an Indian reservation. Bush carried the Fox River Valley, and the eastern half of the state has become fairly solidly Republican. Western Wisconsin, with ailing dairy farms and an economy not so dynamic, has become the Democratic bastion of the state, with metro Madison providing the big Democratic majorities that metro Milwaukee no longer provides in the east. In 2000 Bush ran well ahead of Republican norms in the far north, as he did in the Upper Peninsula of Michigan and northern Minnesota. But in 2004 ancestral Democrats in this north country went back to Kerry, providing votes essential to keeping the state in the Democratic column. The Bush campaign in 2004 succeeded in increasing his popular vote margins in eastern Wisconsin, around Wausau and also in suburban Minneapolis-St. Paul. But Democrats held steady or better in western Wisconsin and increased their margins by 28,000 in Milwaukee County and 25,000 in Madison’s Dane County. Those margins kept Wisconsin in the Democratic column.

Wisconsin once had one of the nation’s most influential presidential primaries. It knocked Wendell Willkie out of the race in 1944, helped John F. Kennedy establish his lead over Hubert Humphrey in 1960, prompted Lyndon B. Johnson to withdraw as Eugene McCarthy was about to beat him here in 1968 and gave George McGovern his first victory in 1972. After that Wisconsin’s primary, even after it was moved from April to March, tended to be ignored. So in 2003 the legislature moved the date up another month to Feb. 17, 2004—the only primary held that day. Wisconsin saw heavier campaigning than it had in years, at least for a few days. It may have proved crucial. John Kerry led John Edwards 40 percent to 34 percent, with Howard Dean in third place with only 18 percent. Kerry ran stronger among self-identified Democrats, Edwards better with Independents and Republicans, who made up 40 percent of primary voters; Wisconsin does not have party registration and few people bothered to vote in the uncontested Republican primary. Edwards carried only 12 of 72 counties (and tied in one other) and did not do as well as he might have hoped in rural areas but, evidently with help from Independents and Republicans, he did carry the Milwaukee suburbs. After Wisconsin, Dean went back to Vermont and ended his campaign, while Edwards failed to get the momentum an early victory here might have given him.

In 2008, Barack Obama defeated Hillary Rohdam Clinton, 58 percent to 41 percent in the state's Feb. 19 contest. John McCain won the Republican primary with 55 percent of the vote.